Fingerprint sensing and matching is a reliable and widely used technique for personal identification or verification. In particular, a common approach to fingerprint identification involves scanning a sample fingerprint or an image thereof and storing the image and/or unique characteristics of the fingerprint image. The characteristics of a sample fingerprint may be compared to information for reference fingerprints already in a database to determine proper identification of a person, such as for verification purposes.
A particularly advantageous approach to fingerprint sensing is disclosed in U.S. Pat. No. 5,953,441 to Setlak and assigned to the assignee of the present invention. The fingerprint sensor is an integrated circuit sensor that drives the user's finger with an electric field signal and senses the electric field with an array of electric field sensing pixels on the integrated circuit substrate. The Setlak patent also discloses an approach to reduce spoofing by sensing another biometric characteristic of the user's finger, in particular, the same electric field sensing pixels are used to determine a complex impedance of the object presented to the sensor. Spoof reduction circuitry determines if the complex impedance of the presented object is indicative of a live finger. In other words, the Setlak patent discloses a biometric authentication approach that relies on multiple biometrics of the user's finger.
Other multi-biometric approaches may use various combinations of voice recognition, facial recognition, fingerprint recognition, and signature dynamics, for example. To satisfy the system, a user must satisfy several of the selected biometrics independently. Such systems may show enhanced selectivity over single biometric systems because false matches in one biometric characteristic are uncorrelated to false matches to a second biometric characteristic. Such a multi-biometric system may be more difficult to spoof, because each of the biometrics needs to be spoofed to compromise the system as a whole.
Representative of multi-biometric systems is, for example, U.S. Patent Application Publication No. 2002/0138768 to Murakami et al. This reference discloses sensing a heartbeat waveform that is substantially, but not necessarily completely unique, as a first biometric trait or characteristic. A second biological trait is used in conjunction with the first biological trait that is preferably also a live physiological trait. Examples of live, potentially substantially unique biological traits include the depth of the various layers of epithelial tissue from a given point on an individual's skin surface. The density of a particular kind of connective tissue, such as bone density, may be another substantially unique histological trait. Likewise, the light absorption characteristics of skin tissue or the visual retinal patterns of an iris could be substantially unique traits. Along these lines, U.S. Patent Application Publication No. 2003/0128867 to Bennett and U.S. Pat. No. 6,483,929 to Murakami et al. both disclose a biometric system that injects infrared energy into the user's finger and senses resulting infrared energy from the user's finger, such as to obtain the user's heartbeat as a biometric.
U.S. Pat. No. 6,327,376 to Harkin discloses a multi-biometric sensor including capacitive sensing pixels below a glass transparent sensing surface for sensing the ridge pattern of the user's finger. The sensor may also include an additional sensor of the contactless kind which relies for its sensing on the use of light, such as visible or infrared light, that can be positioned behind the capacitive fingerprint sensing array.
U.S. Pat. No. 6,560,352 to Rowe et al. discloses a biometric analysis based on using near-ultraviolet, visible, very near-infrared, or near-infrared energy and combinations thereof. U.S. Pat. No. 5,351,303 to Willmore discloses a biometric system that senses and compares the infrared image pattern from an individual's finger to another infrared image pattern of the same finger stored within system memory. Other biometric sensing approaches are also disclosed using ultrasonic imaging, such as U.S. Pat. No. 5,689,576 to Schneider et al. and U.S. Pat. No. 5,737,439 to Lapsley et al., for example.
Unfortunately, the prior art multi-biometric systems may have certain drawbacks. Those having two different sensors are relatively complicated, and may be expensive to install and operate. Those that require multiple presentations of a user's body part, for example, may be inconvenient. The requirement for multiple steps also slows the process. Independent sensors may also be spoofed independently. Of course, there is a continuing need to also further develop even single biometric sensors and systems.
A particularly advantageous approach to multi-biometric fingerprint sensing is disclosed in U.S. Patent Application Publication No. 2005/0089203 to Setlak, which is assigned to the assignee of the present invention and is incorporated in its entirety by reference. The Setlak application discloses a multi-biometric finger sensor sensing different biometric characteristics of a user's finger that have different matching selectivities. The Setlak application also discloses the use of a plurality of biometric sensing pixels to detect a plurality of finger biometric characteristics. Nevertheless, further improvements are still desirable.